1. Field
This invention is in the field of suspending an electrical coil module of an induction furnace in the induction furnace.
2. State of the Art
Induction furnaces are used for many purposes, the main function being heating slab, plate, or ingot steel in steel mills world wide. The furnace can be of many shapes to encompass the size of shapes being heated. The steel shape, generally a slab, plate, or ingot, is run down a roll line where the induction furnace is installed so they pass through the induction coils of the furnace. These slabs, plates, or ingots have cooled down after initial manufacture or casting and must be brought up to a higher temperature in order to facilitate additional manufacturing processes such as rolling, bending, shearing, coiling, etc. The temperature of these pieces must be increased very quickly. This is done inside the induction furnace as each piece proceeds along the roll line through the induction coils inside the furnace. Extreme heat is generated by inducing electrical currents in the steel slab, plate, or ingot by introducing large amount of electrical current into the induction coils via high capacity electrical connections. The coils are supported in coil modules in a furnace housing by rigid support rods secured between the coil modules and the housing. Generally there is a spring mounting of the rods to the furnace housing to absorb vibration.
During the heating process, the coils of the induction furnace are subject to a great amount of vibration caused by cycling of the electrical current. In newer high power furnaces this vibration causes breakage to occur in the support rods connecting the coil modules to the furnace housing and support frame. This breakage occurs after repeated use and usually when one connection fails others will follow until total collapse of an induction coil module occurs resulting in down time of the furnace as well as the whole steel mill roll line and accompanying production capacity. The furnace must be turned off and the induction coil module that has failed removed for immediate rebuilding involving high cost and 24 hour crew loadings. Often times adjacent induction coil modules are also found to be in a state of failure resulting in additional down time and loss of revenue. There is no reliable way to detect or forecast a failure to the connection mechanism of the coil modules to the furnace housing due to massive layers of insulation and sprayed on coating over the modules after the mechanical connections are made during manufacture or repair. Failure is only detected by operators detecting a different sound or by the loose module shorting out and shutting down the system. The operator then has to determine which coil or coils have failed and remove them from the system for repair. Investigation of the failed connections in one steel mill reveals that stress cracking occurs in various places including the support rods and the fasteners securing the support rods to the induction coils. Various remedies have been tried with little appreciable improvement including heavier fasteners, different grades of steel support rods, and varying the electrical current and the on and off cycles of the coils.